NGC 4676: When TADPOLES Collide? (APOD 24 Feb 2008)

[neufer]

http://antwrp.gsfc.nasa.gov/apod/ap020506.html

More like Tadpoles than mice, actually:

. King Lear Act 3, Scene 4
.
EDGAR: Poor Tom; that eats the swimming frog, the toad,
. the *TADPOLE* , the wall-newt and the water; that in
. the fury of his heart, when the foul fiend rages,
. eats cow-dung for sallets; swallows the old rat and
. the ditch-dog; drinks the green mantle of the
. standing pool; who is whipped from tithing to
. tithing, and stock- punished, and imprisoned; who
. hath had three suits to his back, six shirts to his
. body, horse to ride, and weapon to wear;
. But *MICE* and rats, and such small deer,
. Have been Tom's food for seven long year.
------------------------------------------

[Case]

More like Tadpoles than mice

The name Tadpole Galaxy is used for ARP 188, so NGC 4676 needed a different tail inspired name...

[henk21cm]

Either mice of tadpoles, what is happening to these galaxies? The right galaxy seems to be rather intact, at least the rightmost half of it. I imagine that we are aligned in the plane of its spiral arms. The left galaxy has been stripped significantly from its spiral arms, only some stumps remain, close to its center. A symmetry has been broken: why is the right galaxy rather undamaged, whereas the left galaxy has significant damage?.

What puzzles me most is the time scale. The explication says that the process of colliding took several hundreds of million years (0.1Gy), while the rotation of our sun around the center of the galaxy takes about 0.3 Gy. Taking into account Oorts differential rotation, the time scale for rotation must be 0.01 to 0.1Gy. In other words, the rotation of the stars in the spiral arms is relatively fast compared to the time of 'colliding' or interaction. I would have expected a lot more of deformation in the right galaxy than presently visible.

A likely explanation is that the left galaxy grazed (maybe not the correct English word) the right galaxy, just passing the leftmost 'suburbs' of the right galaxy. The cores of both galaxies are rather intact, a fact that interdicts a head on collision of the centers. The plane of the spiral arms of the left galaxy was probably tilted, maybe 45°, compared to the line of sight.


(βατραχομυομαχια the battle between mice and frogs is a parody on Homers Illias. )

[emc]

deleted

[neufer]

More like Tadpoles than mice

The name Tadpole Galaxy is used for ARP 188, so NGC 4676 needed a different tail inspired name...

ARP 188: http://antwrp.gsfc.nasa.gov/apod/ap020506.html
could be named "Cookie Monster" or "Anglerfish"
http://en.wikipedia.org/wiki/Anglerfish

Alternatively,
NGC 4676 : http://antwrp.gsfc.nasa.gov/apod/ap060108.html
could be the pollywogs, polliwogs, polliwigs, porwiggles, or purwiggies.

[emc]

when serpents collide...???

[apodman]

According to

http://en.wikipedia.org/wiki/Batrachomyomachia

Batrachomyomachia, or the Battle of Frogs and Mice attributed to Homer, has come to mean "a silly altercation".

[neufer]

According to

http://en.wikipedia.org/wiki/Batrachomyomachia

Batrachomyomachia, or the Battle of Frogs and Mice attributed to Homer, has come to mean "a silly altercation".

"You callin' me Batrachomyomachic?
"You callin' ME Batrachomyomachic?
"You callin' me BATRACHOMYOMACHIC

[bystander]

Neufer: I think you have your APOD labels wrong. It should be:

NGC 4676: http://antwrp.gsfc.nasa.gov/apod/ap020506.html (Mice)

ARP 188: http://antwrp.gsfc.nasa.gov/apod/ap060108.html (Tadpole)

[neufer]

Either mice of tadpoles, what is happening to these galaxies? The right galaxy seems to be rather intact, at least the rightmost half of it. I imagine that we are aligned in the plane of its spiral arms. The left galaxy has been stripped significantly from its spiral arms, only some stumps remain, close to its center. A symmetry has been broken: why is the right galaxy rather undamaged, whereas the left galaxy has significant damage?.

What puzzles me most is the time scale. The explication says that the process of colliding took several hundreds of million years (0.1Gy), while the rotation of our sun around the center of the galaxy takes about 0.3 Gy. Taking into account Oorts differential rotation, the time scale for rotation must be 0.01 to 0.1Gy. In other words, the rotation of the stars in the spiral arms is relatively fast compared to the time of 'colliding' or interaction. I would have expected a lot more of deformation in the right galaxy than presently visible.

A likely explanation is that the left galaxy grazed (maybe not the correct English word) the right galaxy, just passing the leftmost 'suburbs' of the right galaxy. The cores of both galaxies are rather intact, a fact that interdicts a head on collision of the centers. The plane of the spiral arms of the left galaxy was probably tilted, maybe 45°, compared to the line of sight.

(βατραχομυομαχια the battle between mice and frogs is a parody on Homers Illias. )

I'm *guessing* that the uneffected galaxy is a non rotating & much heavier elliptical galaxy. There exists a null plane between the two galaxies (though closer to the small spiral galaxy) where the stars are in a gravitational balance between the two galaxies. The spiral galaxy stars that rotate into this null plane will never again return to the spiral but will be left behind in a long star trail that will slowly fall into the large elliptical. Stars in the heavier elliptical will undergo a small tidal bulge but will otherwise be unaffected by the encounter.

Code: Select all

.        King Lear  Act 4, Scene 1
.
GLOUCESTER: As flies to wanton boys, are we to the gods.
.	They kill us for their sport.

[henk21cm]

I'm *guessing* that the uneffected galaxy is a non rotating & much heavier elliptical galaxy.

The stars, which bear a resemblence to a spiral arm (right of the rightmost galaxy), what are these? Are these in the the null plane

There exists a null plane between the two galaxies (though closer to the small spiral galaxy) where the stars are in a gravitational balance between the two galaxies.

you refered to?

The spiral galaxy stars that rotate into this null plane will never again return to the spiral but will be left behind in a long star trail that will slowly fall into the large elliptical.

That is a line of thinking which i did not explore. I supposed there were two spiral galaxies. Maybe a simulation will shed some light on this topic. Since i do not know a galactic collision simulation program, i will have to write it. It must be simple, since i can not calculate all stars in a galaxy. My PC isn't 'deep thought'. I was thinking of simplifying the center of the galaxy as one large mass, about 75% of the galactic mass. The stars in the spiral arms as a few hundred (N) individual masses, accounting for the rest of the galaxies mass. That reduces the number of interactions to be handles to about N*N/2. An elliptical system is a bit harder, first try just a central mass.

Stars in the heavier elliptical will undergo a small tidal bulge but will otherwise be unaffected by the encounter.

Agree, since their distance to the center of the galaxy is considerably smaller than the distance between the stars in spiral arms to the center of the spiral galaxy.

[neufer]

I'm *guessing* that the uneffected galaxy is a non rotating & much heavier elliptical galaxy.

The stars, which bear a resemblence to a spiral arm (right of the rightmost galaxy), what are these? Are these in the the null plane

The small spiral has been unraveling for some time (like a small reel of 8mm film rolling across the floor).
Unless your eyes are better than mine all I see is this long unrolled line of small spiral galaxy stars.

There exists a null plane between the two galaxies (though closer to the small spiral galaxy) where the stars are in a gravitational balance between the two galaxies.

you refered to?

The null plane is simply a (small local) plane perpendicular to the (moving) line connecting both galaxies on which a free falling object would be balanced between the attractions of the two galaxies. Back in the Apollo days it was the plane Apollo 11 had to cross to be falling toward the moon on the way out (or falling toward the earth on the way back).

The spiral galaxy stars that rotate into this null plane (region) will never again return to the spiral but will be left behind in a long star trail that will slowly fall into the large elliptical.

That is a line of thinking which i did not explore. I supposed there were two spiral galaxies. Maybe a simulation will shed some light on this topic. Since i do not know a galactic collision simulation program, i will have to write it. It must be simple, since i can not calculate all stars in a galaxy. My PC isn't 'deep thought'. I was thinking of simplifying the center of the galaxy as one large mass, about 75% of the galactic mass. The stars in the spiral arms as a few hundred (N) individual masses, accounting for the rest of the galaxies mass. That reduces the number of interactions to be handles to about N*N/2. An elliptical system is a bit harder, first try just a central mass.

Unfortunately "simplifying the center of the galaxy as one large mass" was found to be a flawed assumption due to the neglect of dark matter:
http://en.wikipedia.org/wiki/Galaxy_rotation_problem

Stars in the heavier elliptical will undergo a small tidal bulge but will otherwise be unaffected by the encounter.

Agree, since their distance to the center of the galaxy is considerably smaller than the distance between the stars in spiral arms to the center of the spiral galaxy.

[Qev]

A Java applet galaxy collision simulator. It's no supercomputer, but it's still nifty.

http://burro.astr.cwru.edu/JavaLab/GalC ... /main.html

[fotobits]

http://www.ifa.hawaii.edu/~barnes/resea ... index.html

The page above includes three simulations of NGC 4676. This particular pair has had me fascinated since 1986 when I saw through a 20-inch Obsession telescope. There was very little information about The Mice back then. Now, thanks to the Internet, HST and newfangled computers we know quite a bit more about this fascinating object.

[henk21cm]

Although deviating from the original topic: the mice, dark matter seems to be a key argument in galactic collisions. Energy and momentum of each galaxy is transfered into internal motion, due to dark matter. This leads to a larger relative occurence of merging galaxies than would have been visible without the dark matter. The simulations Qev and fotobits have provided, gave me an entirely new insight in the dynamics of a collision.

Art Neufer pointed out that a central mass for the center of the galaxy is a flawed option, due to dark matter. Observations of the rotational velocities of stars in the spiral arms indicate non Keplerian orbits. When the orbital velocities are roughly constant as a function of distance to the center of the galaxy, the arms will develop a spiral shape, like the frontal cloud band of a low pressure system. The outer stars move the same distance in the same amount of time as the inner stars, yet the angular displacement of outer stars is less than that of the inner stars. This is more or less the Oort model.

In stead of answering questions, science states that each new fact or observations reveals more questions. Indeed! How about the distribution of dark matter and the ratio between dark and foton emitting matter? If the bulk of dark matter is located near the center of the galaxy, Keplerian orbits are to be expected. If the density of dark matter is constant as a function of distance from the center of a galaxy, the bulk of the mass of dark matter is concentrated at he edges or outer parts of the galaxy. (mass in a shell: 4πr×r×dr). When the amount of dark matter is large compared to the foton emitting mass in the spiral arms, the rotation of the spiral arms will be dominated by the dark mass.

So how much mass is needed, to explain the roughly constant velocity in the spiral arms?